In hindsight, Moriarty was kind of wasted in the Librarians. Or, more accurately, the entire second season was really humiliating to him.
You see, professor Moriarty doesn't dirty his hands. Ever. He's a criminal mastermind ruling over the entire London underworld, if not more, and he never acts directly. The twice he met Sherlock were the most direct thing he did. And throughout season 2 of the Librarians, he's a lackey to Prospero and effectively the one doing his dirty job for him. No wonder he's chafing against that. If one wonders about it, it is why Prospero is using him that way. The answer, IMO, is the stable timeloop. Prior to summoning him, I'm not certain Prospero would've known Moriarty is the one who tried to hinder him in the past. After he did, however... I won't be surprised to learn that he started to mistreat him. Especially seeing the people who drowned his book and broke his staff. The only question I have is why Prospero claimed Shakespeare did that.
